I am using the path planning in calculation modules for mobile robot. However, the path result is different every time. How can I set the function to get the same path result all the time? Because I need the same path to do the experiment.

I added path planning task in calculation modules, then used the function, simSearchPath, in child script to plan the path.

Thank you for your replying.
I'm using OMPL motion planning, RRT Connect Algorithm. I implemented the same code from the demo, 3DoFHolonomicPathPlanning, but there is an error that I don't know how to solve it.
[0m[31mError: RRTConnect: Motion planning start tree could not be initialized!
at line 177 in E:\ompl-1.3.1-Source\src\ompl\geometric\planners\rrt\src\RRTConnect.cpp